Excess body fat is an important cause of human disease, disability, and cosmetic disturbance. For many people excess body fat is also a source of psychosocial distress and reduced self-esteem.
Excess body fat may be diffuse or concentrated on particular portion(s) of the body. Of particular importance is excess body fat of the face, for example, of the eyelids, chin, or jowls. Other important sites of excess body fat can include, for example, the arms, abdomen, buttocks, hips, chest, thighs, and neck. Excess body fat can also involve excessive breast tissue on a woman or on a man, i.e., gynecomastia. Excess body fat can be located within or near the eyelids, and topical treatment of such fat requires a composition that is safe for application near the eyes, i.e. an ophthalmic and/or ophthalmically compatible formulation. Local accumulations of body fat may result from constitutional factors, disease, hormonal status, or as side effects of medication or other substances. Even in the absence of disease, cosmetic considerations apply to individuals who nevertheless perceive an excess of fat and wish to have it corrected. For example, excess submental fat, commonly known as “double chin,” is not considered a disease; however, people with excess submental fat often appear less attractive and less youthful, and can have lower self-esteem as a result. Likewise, an individual may have excess subcutaneous fat on the anterior abdomen, excess subcutaneous fat on the oblique abdomen, e.g. above the iliac crests (“love handles”), excess chest fat, excess breast fat, excess buttocks fat, excess hip fat, excess thigh fat, excess leg fat, excess upper arm fat, excess check fat, excess neck fat, etc.
A number of medical conditions are considered to be causes of excess body fat. Examples include drug-induced obesity, hypothyroidism, pseudohypoparathyroidism, hypothalamic obesity, polycystic ovarian disease, depression, binge eating, Prader-Willi syndrome, Bardet-Biedl syndrome, Cohen syndrome, Down syndrome, Turner syndrome, growth hormone deficiency, growth hormone resistance, and leptin deficiency or resistance. Disfiguring excess regional fat deposits, for example excess dorsocervical fat, may be found in conditions such as HIV lipodystrophy, Cushing syndrome and pseudo-Cushing syndrome (i.e., characteristic syndrome of excess body fat and other findings due to excessive endogenous or exogenous corticosteroid levels), other acquired lipodystrophies, familial lipodystrophies, lipoma, lipomatosis, and Madelung disease.
Medications known to cause excess body fat include cortisol and analogs, other corticosteroids, megace, sulfonylureas, antiretrovirals, tricyclic antidepressants, monoamine oxidase inhibitors, selective serotonin reuptake inhibitors, oral contraceptives, insulin, risperidone, clozapine, and thiazolidinediones.
Changes in hormonal status, including physiologic changes such as pregnancy or menopause, may result in excess body fat in a subject. Smoking cessation commonly leads to weight gain and excess body fat. Trauma may favor the accumulation of excess body fat by virtue of immobility or disuse of an extremity. Similar problems may affect a subject who is immobilized, for example due to an injury. Some tumors, for example lipomas and liposarcomas, are characterized by local collections of fat cells. Lipomatosis is any condition characterized by the formation of multiple lipomas on the body, e.g., familial multiple lipomatosis, adiposis dolorosis (Dercum's disease), pelvic lipomatosis, etc.
Even in the absence of underlying pathology, an individual may have cosmetic concerns about local or diffuse deposits of body fat. These can usually be attributed to constitutional or hereditary factors, developmental history, age, gender, diet, alcohol use, or other components of lifestyle. Individuals in such circumstances commonly wish to reduce the amount of fat on the face, eyelids, chin, arms, neck, abdomen, chest, breast, buttocks, hips, thighs, and/or legs. In some cases a local excess of fat can be due to fat prolapse, displacement, and/or migration, as in age-related orbital fat prolapse or descent of malar fat pads. Grave's ophthalmopathy (thyroid-related eye disease) is a condition that can be treated by reducing the volume of orbital fat.
A number of methods have been developed to reduce or remove excess body fat. It is helpful to classify these methods as extractive, metabolic, or adipolytic. Extractive methods, such as lipoplasty (e.g., liposuction) or local excision, are methods whereby fat is physically removed from areas of interest. Such methods are costly and may involve scars, postsurgical deformity or regression, discomfort, infection, and other adverse reactions.
In contrast to extractive methods, metabolic methods, which include systemic medications, nutritional supplements, devices, and exercise or other body treatment, seek to modify the subject's metabolism (e.g., whether caloric consumption, expenditure, or both) such that the subject incurs a net loss of fat. A disadvantage is that these methods typically cannot be directed to a particular part of the body. Another drawback is potential concomitant loss of water, carbohydrates, protein, vitamins, minerals, and other nutrients. Furthermore, traditional diet medications may have undesired side effects, for example palpitations, tremor, insomnia, and/or irritability in a subject who uses stimulants as appetite suppressants. Despite salubrious value, the traditional metabolic methods of diet and exercise are not practical for everybody.
Adipolytic methods aim to cause breakdown of adipocytes and/or their lipid contents. For example, fat deposits can be reduced by exposure to cold temperature or to deoxycholate, a solubilizer that lyses cell membranes and results in local necrosis. Drawbacks of these methods can include poor discrimination between adipose and other nearby tissues, barriers to delivery that require hypodermic needles or special equipment, and adverse effects such as necrosis, inflammation, and pain.
Compounds of the prostaglandin FP receptor agonist (PFPRA compound) class, e.g., latanoprost and tafluprost, can be administered to the skin to locally reduce adipose tissue under the skin, i.e., subcutaneous fat. See, e.g., U.S. Pat. No. 8,426,471 and U.S. Publication No. 20100234466, incorporated herein by reference. Developing topical delivery of the PFPRA compound poses significant challenges, since delivery to subcutaneous fat comprises delivery across the stratum corneum, epidermis, dermis, and dermal microcirculation, and into the fat below.
For example, the skin, in particular the stratum corneum, presents a formidable physical barrier to drug penetration. See, e.g., Dayan N, Delivery System Design in Topically Applied Formulations: An Overview, in Rosen M, Delivery System Handbook for Personal Care and Cosmetic Products, William Andrew, 2005, pp. 103-104. For any particular drug, the formulation must be selected empirically. The formulation must be physically and chemically compatible with the drug.
Furthermore, provided that a formulation enables a drug to cross the skin, to reach the subcutaneous fat it must also circumvent what is known as the “sink condition” of the dermal circulation. See, e.g., Dayan N, Delivery System Design in Topically Applied Formulations: An Overview, in Rosen M, Delivery System Handbook for Personal Care and Cosmetic Products, William Andrew, 2005, pp. 103-104; Kao J, In Vitro Assessment of Dermal Absorption, in Hobson D W, Dermal and Ocular Toxicology: Fundamentals and Methods, CRC Press, 1991, pp. 272-273. Because the dermis is invested by a network of capillaries with rapid blood flow, for any solute (e.g., drug) that penetrates the dermis, a wide concentration gradient is created between the skin and bloodstream. Thus, there is a strong tendency for drugs that penetrate into the dermis to diffuse rapidly down this gradient into the bloodstream. This sink phenomenon favors systemic delivery (e.g., to the bloodstream, as with a nicotine patch), but undermines attempts at local delivery (e.g., to subcutaneous fat, as in the present invention). No method of reasoning or prediction is available in the art to suggest which formulations, if any, can circumvent the sink condition. Therefore, the artisan must search for such formulations empirically, and without prior knowledge that such formulation even exists.
The formulation must also have a favorable systemic drug exposure profile, e.g., that avoids excessive levels of drug in the bloodstream. This requirement is rendered more difficult by the sink condition.
Additionally, the formulation should deliver the active ingredient with reasonable efficiency. One measure of efficiency is the ability to minimize the concentration of active ingredient in the finished product and still maintain the desired therapeutic effect. This has implications for manufacturability, cost of goods, and local safety and tolerability. Another measure of efficiency is the ability to minimize the dose frequency and still maintain the desired therapeutic effect, which has implications for patient convenience and product marketability.
As well, the formulation must cause little or no skin irritation. If applied to skin near the eye, e.g., the eyelid, the formulation is considered an ophthalmic formulation. Generally, an ophthalmic formulation must be sterile, e.g., according to Chapter <71> of the U.S. Pharmacopeia. Preferably, an ophthalmic formulation must also be free or essentially free of bacterial endotoxin, e.g. according to Chapter <85> of the U.S. Pharmacopeia, e.g., an endotoxin level of <10 EU (endotoxin units) per gram of composition. If applied to skin near the eye, the formulation must be ophthalmically compatible, i.e., the formulation must not cause clinically significant eye irritation, and must not be toxic to the eye, e.g., the ocular surface, e.g. the cornea. Irritation potential and ocular toxicity are studied empirically by standard preclinical models, or in human trials. Although the skin or eye irritation potential of individual inactive ingredients is generally known, combinations of inactive and active ingredients can cause unexpected irritation, which must be tested empirically.
Furthermore, the formulation must possess other qualities necessary to make a topical formulation and market it to consumers: ease of manufacture, physical and chemical stability, and commercially acceptable appearance, odor, and tactile qualities.
Therefore, there is a need for new compositions for topically delivering a PFPRA compound to adipose tissue under the skin.